Growing recognition of hearing loss produced by excessive noise has increased the demand for hearing protectors and has accelerated improvements in their performance. Three types of hearing protectors have become known in the field; namely, i) earplugs that are inserted into the ear canal, ii) semi-inserts that seal the ear canal at its entrance, and iii) ear muffs that cover the entire outer ear. Each of the foregoing types of device has its own advantages and disadvantages. That is, earplugs are small and cheap on a unit basis and provide reasonable noise reduction when properly used. However, these devices pose hygiene problems due to the sensitivity of the ear canal to infection. Earplugs also tend to impact the ear canals with cerumen and become uncomfortable when worn over extended periods of time. These devices are also expensive in practical use because they have to be replaced often. Passive earmuffs can be very effective at high sound frequencies, but these devices provide inherently little noise reduction at low frequencies. Earmuffs are the most expensive and the most cumbersome of the devices in use. Introduction of an electro-acoustic feedback has improved their performance at low sound frequencies, but made the earmuffs more expensive and cumbersome. These devices also have the tendency to heat up the head, especially, in warm weather, creating additional discomfort for the wearer. Semi-inserts avoid the problems of earplugs because they do not enter the ear canal. They also are cheaper and much less cumbersome than earmuffs. Traditionally, however, these devices have provided the least noise reduction of the three noted types.
More recently, and as described in U.S. Pat. No. 5,824,967, Applicant has applied a new principle to semi-insert ear defenders. According to this principle and instead of closing the ear canal with a solid plug, a pair of tubes, referred to as “muffler tubes”, are connected to the ear canal on each side of the head by means of a resilient cuff providing a tight seal around the ear canal. High noise reduction is achieved by making the acoustic impedance at the entrance of the tube much lower than the acoustic impedance at the entrance of the ear canal, such that acoustic energy flows into the tube rather than into the ear canal. The relatively low impedance can be produced in two cooperative ways—by making the tubes wider than the ear canals and by making their length equal to a quarter wave length of sound at medium audible frequencies. The bandwidth of the low impedance is increased by appropriate distribution of sound absorbing material in the tubes. The semi-inserts according to this design provide attributes making them desirable in that they are comfortable, less cumbersome than earmuffs, and can provide the highest noise reduction achieved thus far by any type of hearing protectors. These devices allow the noise reduction to be nearly evenly distributed over the audible frequency range, assuring optimum speech communication and music reception in noise.
In spite of the improvements that have been obtained by the new design, these semi-inserts have two known disadvantages. First, they may become cumbersome when helmets or hats are worn. Second, the long muffler tubes have been found not to be aesthetic by some wearers.